Individualized Dosimetry for Holmium-166 Radioembolization in Patients With Unresectable Hepatocellular Carcinoma

The goal of this clinical trial is to test the safety and effectiveness of a medical device called 166-Holmium microspheres (QuiremSpheres®) in patients with hepatocellular carcinoma (HCC) . The main questions it aims to answer are: * What is the safety and toxicity profile of the 166-Holmium microspheres? * Is the device effective in treating HCC? Participants will undergo a range of screening procedures to confirm they are eligible and to record their baseline results, including: * A Computed Tomography (CT) scan * A Magnetic Resonance Imaging (MRI) scan * Blood tests * Quality of life questionnaires Before receiving treatment with QuiremSpheres® the participant will receive a 'scout' dose of the microspheres, to check whether there is distribution of the radioactivity to other non-target areas of the body. This is measured using Single-Photon Emission Computed Tomography-CT imaging. If the distribution to non-target areas is deemed to not be too high, the participant will go on to receive the individualised therapeutic dose of QuiremSpheres®. Follow-up visits will occur 3 and 6 weeks post-treatment dose, and then at 3 and 6 months.